This invention relates to a sealing apparatus for picture tubes adapted to seal a glass bulb having a phosphor screen on the inner side thereof, and a stem structure having an electron gun structure mounted thereon.
In general, in a step of manufacturing a color picture tube, a phosphor screen, a graphite electrode and a shadow mask are set on the inner side of a glass bulb, and an electron gun structure-mounted stem structure is then sealed to an open end of a neck portion of the glass bulb. Such a sealing operation is disclosed in, for example, Japanese Patent Publication No. 31595/1978. In order to carry out such a picture tube sealing operation, a picture tube sealing apparatus, which will be described in the following paragraph, is used.
FIG. 2 is a construction diagram in plan of a principal portion of an example of a generally-used picture tube sealing apparatus. Referring to the same drawing, a disc type turntable 10 is provided on the outer circumferential portion thereof with a plurality of sealing holders 11, which are adapted to hold this type of glass bulbs concentrically with their tubular shafts, and which are spaced at regular intervals. These sealing holders 11 are turned at a predetermined speed in the direction of an arrow A by an automatic driving unit (not shown in the drawing). The sealing holders 11 are moved accurately to predetermined places at regular time intervals by an index driving unit (not shown in the drawing). On this turntable 10, the mounting and demounting of glass bulbs are done usually in the sealing holders 11 in places #1-#2; the preheating of the neck portions and the portions to be sealed of the glass bulbs, in the sealing holders 11 in places #3-#8; the fusing of the neck portion of the glass bulb, in the sealing holder 11 in a place #9; the melt-separating of the glass bulb, in the sealing holder in a place #10, the gradual cooling of the neck portions of the glass bulbs in the sealing holders in places #11-#15; and then the removing of fragment of the neck tube (usually called cullet glass) in the sealing holder in a place #16, which has been separated from the neck portion of the glass bulb by the melt-separating.
FIG. 3 is a side elevation of a principal portion of the sealing holder 11 illustrated in FIG. 2. Referring to FIG. 3, the sealing holder 11 is adapted to retain firmly in a predetermined reference point a glass bulb 1, in which a phosphor screen, a graphite electrode and a shadow mask etc. are formed, by a bulb holder unit 17 consisting of a bulb stopper 12, a panel chuck 13, a bulb support 14, a holder frame 15 and a bulb holder 16 etc., and supported fixedly on the turntable 10 via a support 18. A mount pin 19 which is provided with a stem structure 3 having an electron gun structure 2 mounted thereon concentrically with a tubular shaft thereof to drive the stem structure 3 in the rotational and vertical directions is joined to the lower portion of this bulb holder unit 17. Reference numeral 1 denotes a glass bulb.
In this arrangement, the stem structure 3 on which the electron gun structure 2 is mounted is roughly regulated and set on the mount pin 19, and then lifted and inserted into the bulb neck portion 1a. The mount pin 19 is regulated finely in the rotational and vertical directions to position the electron gun structure 2 to a predetermined height. The part of the outer circumferential surface of the neck portion 1a which is opposed to the stem glass 3a in the stem structure 3 is then heated with the flames 21 generated by gas burners 20, as shown in FIG. 4, to weld the neck portion 1a and stem glass 3a to each other as shown by a solid line. The neck portion 1a and stem glass 3a are thus welded and sealed and simultaneously the cullet glass 1a' is melted and separated from the neck portion 1a, which hangs down from the welded portion. The melted and separated cullet glass 1a' is left on a base 19a of the mount pin 19. Reference numeral 3b denotes an exhaust tube.
There are various types of picture tubes, such as a picture tube in which the outer diameter of a bulb neck portion 1a is, for example, 29 mm (which will hereinafter be referred to as a 29 mm neck-carrying picture tube), a 22 mm picture tube (which will hereinafter be referred to as a 22 mm neck-carrying picture tube) and a 38 mm neck-carrying picture tube. The demand ratio of these neck-carrying picture tubes has recently become unstable. Accordingly, for example, a 29 mm neck-carrying picture tube and a 22 mm neck-carrying picture tube have their special sealing apparatus. This sealing apparatus has a satisfactory overall sealing capability but, for example, when the demand ratio of the 29 mm neck-carrying picture tubes and 22 mm neck-carrying picture tubes increases or decreases extremely, the sealing capability of the apparatus becomes low.
To be concrete, this sealing apparatus has a special gas burner 20 shown in FIG. 5. In order to apply a gas burner specially used for a 29 mm neck-carrying picture tube to a 22 mm neck-carrying picture tube, or a gas burner specially used for a 22 mm neck-carrying picture tube to a 29 mm neck-carrying picture tube, the diameter of a flame 21 of the burner 20 is regulated manually so that the flame 21 sufficiently covers the region to be heated of the bulb neck portion 1a, in accordance with the different outer diameter thereof to thereby set the heating power to a suitable level. Namely, in order to heat the neck portion 1a of the 29 mm neck-carrying picture tube, the diameter of the flame 21 is increased so as to increase the heating power, and, in order to heat the neck portion 1a of the 22 mm neck-carrying picture tube, the diameter of the flame 21 is set smaller than that in the case of heating the neck portion 1a of 29 mm in diameter, by changing the nozzle of the gas burner 20.